The present invention relates to a Radio Frequency Identification tag, to a Radio Frequency Identification reader, and to a method for recognizing at least one Radio Frequency Identification tag.
Radio Frequency Identification (RFID) is an automatic identification system that uses wireless communications to identify objects. Nowadays, large amounts of RFID tags are used in supply chains for product identification or sensor networks (see e.g. G. Vannucci, A. Bletsas, and D. Leigh, A Software-Defined Radio System for Backscatter Sensor Networks, IEEE Transactions on Wireless Communications, vol. 7, pp. 2170-2179, 2008), especially, where the cost and energy are critical.
One of the biggest RFID challenges is the capability to resolve tag collisions.
All RFID tags within the reading area of a reader are scheduled using Frame Slotted Aloha (FSA). As a result, only a single tag response can be decoded successfully at a time.
The RFID tags select random slots. Nevertheless, when multiple tags reply simultaneously within the same slot, a collision occurs and the slot is discarded (see e.g. M. V. Bueno-Delgado, J. Vales-Alonso, and F. J. Gonzalez-Castaño, Analysis of DFSA Anti-collision Protocols in passive RFID environments, 35th Annual Conference of IEEE Industrial Electronics, pp. 2610-2617, 2009). Hence, either the recognition time increases or less RFID tags are recognized.
In UHF RFID systems, the rate of the tag replies variations are much more crucial than in other communication systems. In the EPCglobal Class-1 Gen-2 RFID protocol, this tag reply rate is called Backscatter Link Frequency (BLF, see EPC™ Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960 MHz, Version 1.2.0, EPCglobal Inc., 2007).
The US 2011/0148599 A1 suggests to allocate the RFID tags to different groups in order to reduce the chance of collisions. The RFID tags just reply to a query command after their group has received a so called wake-command.
Thus, an object of the invention is to improve the detection of RFID tags of a plurality of RFID tags in the vicinity of an RFID reader.